The present invention generally relates to methods for the monitoring of fluids in or near real-time, and, more specifically, to methods for monitoring fluids prior to, during or after their introduction into a subterranean formation and/or to methods for monitoring produced fluids from a subterranean formation.
When conducting operations within a subterranean formation, it can be important to precisely know the characteristics of a fluid or other component present in or being introduced into the formation. Typically, the analysis of fluids and other components being introduced into a subterranean formation has been conducted off-line using laboratory analyses (e.g., spectroscopic and/or wet chemical methods). These analyses can be conducted on fluid samples being introduced into the subterranean formation or on flow back fluid samples being produced from the subterranean formation after a treatment operation has occurred. Depending on the analysis needed, such an approach can take hours to days to complete, and even in the best case scenario, a job can often be completed prior to the analysis being obtained. Furthermore, off-line laboratory analyses can sometimes be difficult to perform, require extensive sample preparation and present hazards to personnel performing the analyses. Bacterial analyses can particularly take a long time to complete, since culturing of a bacterial sample is usually needed to obtain satisfactory results.
Although off-line, retrospective analyses can be satisfactory in certain cases, they do not generally allow real-time or near real-time, proactive control of a subterranean operation to take place. That is, off-line, retrospective analyses do not allow active control of a subterranean operation to take place, at least without significant process disruption occurring while awaiting the results of an analysis. In many subterranean operations, the lack of real-time or near real-time, proactive control can be exceedingly detrimental to the intended outcome of the subterranean operation. For example, if an incorrect treatment fluid is introduced into a subterranean formation, or if a correct treatment fluid having a desired composition but at least one undesired characteristic (e.g., the wrong concentration of a desired component, the wrong viscosity, the wrong pH, an interfering impurity, a wrong sag potential, the wrong kind or concentration of proppant particulates, bacterial contamination and/or the like) is introduced into a subterranean formation, the subterranean operation can produce an ineffective outcome or a less effective outcome than desired. Worse yet, if an incorrect treatment fluid or a treatment fluid having an undesired characteristic is introduced into the subterranean formation, damage to the formation can occur in some cases. Such damage can sometimes result in the abandonment of a wellbore penetrating the subterranean formation, or a remediation operation can sometimes be needed to at least partially repair the damage. In either case, the consequences of introducing the wrong treatment fluid into a subterranean formation can have serious financial implications and result in considerable production delays.
Off-line, retrospective analyses can also be unsatisfactory for determining the true suitability of a treatment fluid for performing a treatment operation or for evaluating the true effectiveness of a treatment operation. Specifically, once removed from their subterranean environment and transported to a laboratory, the characteristics of a treatment fluid sample can change, thereby making the properties of the sample non-indicative of the true effect produced by the treatment fluid in the subterranean formation. Similar issues also can be encountered in the analysis of treatment fluids before they are introduced into a subterranean formation. That is, the properties of the treatment fluid can change during the lag time between collection and analysis. In such cases, a treatment fluid that appears unsuitable for subterranean use based upon its laboratory analysis could have been suitable if introduced into the subterranean formation at an earlier time. The converse can also be true. Factors that can alter the characteristics of a treatment fluid during the lag time between collection and analysis can include, for example, scaling, reaction of various components in the fluid with one another, reaction of various components in the fluid with components of the surrounding environment, simple chemical degradation, and bacterial growth.
In addition, the monitoring of source materials that are being used in the formation of a treatment fluid can also be of interest. For example, if an incorrect source material or the wrong quality and/or quantity of a source material is used to form a treatment fluid, it is highly likely that the treatment fluid will have an undesired characteristic. In this regard, monitoring of a source material can also be an important quality control feature in the formation of a treatment fluid.
In addition to monitoring the characteristics of treatment fluids that are being introduced into a subterranean formation, the monitoring of fluids produced from a subterranean formation can also be of considerable interest. Produced fluids of interest can include both native formation fluids and flow back fluids produced after the completion of a treatment operation. As noted previously, the characteristics of a flow back fluid can provide an indication of the effectiveness of treatment operation, if analyzed properly. In spite of the wealth of chemical information that can be present in these fluids, it has sometimes been conventional in the art to simply dispose of produced formation water or flow back fluids resulting from a treatment operation. As an added concern, the significant volumes of fluids produced from a subterranean formation can present enormous waste disposal issues, particularly in view of increasingly strict environmental regulations regarding the disposal of produced water and other types of waste water. The inability to rapidly analyze produced fluids can make the recycling or disposal of these fluids exceedingly problematic, since they must be stored until analyses can be completed. As previously indicated, even when an analysis has been completed, there is no guarantee that the sample will remain indicative of the produced bulk fluid.
More generally, the monitoring of fluids in or near real-time can be of considerable interest in order to monitor how the fluids are changing with time, thereby serving as a quality control measure for processes in which fluids are used. Specifically, issues such as, for example, scaling, impurity buildup, bacterial growth and the like can impede processes in which fluids are used, and even damage process equipment in certain cases. For example, water streams used in cooling towers and like processes can become highly corrosive over time and become susceptible to scale formation and bacterial growth. Corrosion and scale formation can damage pipelines through which the water is flowing and potentially lead to system breakdowns. Similar issues can be encountered for fluids subjected to other types of environments.
Spectroscopic techniques for measuring various characteristics of materials are well known and are routinely used under laboratory conditions. In some cases, these spectroscopic techniques can be carried out without using an involved sample preparation. It is more common, however, to carry out various sample preparation steps before conducting the analysis. Reasons for conducting sample preparation steps can include, for example, removing interfering background materials from the analyte of interest, converting the analyte of interest into a chemical form that can be better detected by the chosen spectroscopic technique, and adding standards to improve the accuracy of quantitative measurements. Thus, there can be a delay in obtaining an analysis due to sample preparation time, even discounting the transit time of the sample to a laboratory. Although spectroscopic techniques can, at least in principle, be conducted at a job site or in a process, the foregoing concerns regarding sample preparation times can still apply. Furthermore, the transitioning of spectroscopic instruments from a laboratory into a field or process environment can be expensive and complex. Reasons for these issues can include, for example, the need to overcome inconsistent temperature, humidity and vibration encountered during field or process use. Furthermore, sample preparation, when required, can be difficult under field analysis conditions. The difficulty of performing sample preparation in the field can be especially problematic in the presence of interfering materials, which can further complicate conventional spectroscopic analyses. Quantitative spectroscopic measurements can be particularly challenging in both field and laboratory settings due to the need for precision and accuracy in sample preparation and spectral interpretation.